Detailed Explanation for this Vulnerability Test
The remote host is affected by the vulnerability described in GLSA-200505-10
(phpBB: Cross-Site Scripting Vulnerability)

phpBB is vulnerable to a cross-site scripting vulnerability due to
improper sanitization of user supplied input. Coupled with poor
validation of BBCode URLs which may be included in a forum post, an
unsuspecting user may follow a posted link triggering the
vulnerability.

Impact

Successful exploitation of the vulnerability could cause arbitrary
scripting code to be executed in the browser of a user.